Diabetes is a major public health concern because of its increasing prevalence and associated health risks. The disease is characterized by high levels of blood glucose resulting from defects in insulin production, insulin action, or both. Two major forms of diabetes are recognized, type I and type II. Type I diabetes develops when the body's immune system destroys pancreatic beta cells, the only cells in the body that make the hormone insulin that regulates blood glucose. To survive, people with type I diabetes must have insulin delivered by injection or a pump. Type II diabetes (T2D) accounts for about 90 to 95 percent of all diagnosed cases of diabetes. Type II diabetes usually begins as insulin resistance, a disorder in which the cells do not use insulin properly. Key target tissues, including liver, muscle, and adipose tissue, are resistant to the effects of insulin in stimulating glucose and lipid metabolism. As the need for insulin rises, the pancreas gradually loses its ability to produce insulin. Controlling type II diabetes with medication is essential; otherwise, it can progress into pancreatic beta-cell failure requiring complete dependence on insulin.
Several drugs in five major categories, each acting by different mechanisms, are available for treating hyperglycemia and subsequently, T2D (Moller, D. E., “New drug targets for Type II diabetes and the metabolic syndrome” Nature 414; 821-827, (2001)): (A) Insulin secretogogues, including sulphonyl-ureas (e.g., glipizide, glimepiride, glyburide) and meglitinides (e.g., nateglidine and repaglinide), dipeptidyl peptidease IV (DPP-IV) inhibitors (e.g., those in WO2005116014, sitagliptin, vildagliptin, alogliptin, dutogliptin, linagliptin, and saxogliptin), and glucagon-like peptide 1 (GLP-1) agonists (e.g, liraglutide, albiglutide, exenatide (Byetta®), albiglutide, lixisenatide, dulaglitide, semaglutide) enhance secretion of insulin by acting on the pancreatic beta-cells. (B) Biguanides (e.g., metformin) are thought to act primarily by decreasing hepatic glucose production. Biguanides often cause gastrointestinal disturbances and lactic acidosis, further limiting their use. (C) Inhibitors of alpha-glucosidase (e.g., acarbose) decrease intestinal glucose absorption. These agents often cause gastrointestinal disturbances. (D) Thiazolidinediones (e.g., pioglitazone, rosiglitazone) act on a specific receptor (peroxisome proliferator-activated receptor-gamma) in the liver, muscle and fat tissues. They regulate lipid metabolism subsequently enhancing the response of these tissues to the actions of insulin. Frequent use of these drugs may lead to weight gain and may induce edema and anemia. (E) Insulin is used in more severe cases, either alone or in combination with the above agents.
Ideally, an effective new treatment for T2D would meet the following criteria: (a) it would not have significant side effects including induction of hypoglycemia; (b) it would not cause weight gain; (c) it would at least partially replace insulin by acting via mechanism(s) that either increase endogenous insulin secretion or are independent from the actions of insulin; (d) it would desirably be metabolically stable to allow less frequent usage; and (e) it would be usable in combination with tolerable amounts of any of the categories of drugs listed herein. There continues to be a need for new effective treatments for T2D.